After contacting the owner of the company who makes the amp boards(Tom, who seems like a really nice guy), I ordered a large toroidal transformer (1000VA), heavy duty power supply, and two amplifier modules which should output 500W each easily when bridged. Since they are Class D, they are much more efficient (>90% vs 50-60% for class A/B) and should put out much less heat. THD numbers look really good too. I should be getting the parts by this weekend and will do a quick assembly first to test things out and see how it sounds. I'll let you guys know how it goes.

Yep, they're in my bookmarks (as well as some others). Sure Electronics output power was much lower, and the THD+N at rated power was REALLY high (10%). THD+N at rated power for the modules I bought is <1%.

You're basically on your own for the case, but just about any enclosure would work. For now, I'm just going to assemble it on a block of wood. If it sounds great (like most have said), I'll probably build a nice wood enclosure.

Tom also buys in bulk and will pass the savings on to you. The 1000VA toroidal transformer would go for $100 alone unshipped if I tried to buy it myself (sucker weighs in at 18 lbs alone).

Read through the thread link I posted above if you get a chance. There are some wonderful examples of systems put together, as well as some nice DIY cases. I'm pretty excited about this...

Will do. It's shipping today so I should have the parts by Friday. The first assembly will be quick and dirty just to get it going and test it out (it will be ugly to look at). It should not take more than a couple of hours to do this, so I should have my initial impressions this weekend (I wish I had a THD analyzer!). I think I may wind up buying a clamp on ammeter to measure amp current draw and use my sound meter to measure db output. I know this amp will use less power to get the same db output, but I would love to take some measurements against my AVR-3806. I do have an infrared thermometer, so I'll shoot the heatsink to see how hot it gets (open air).

The final assembly (time and money involved) will depend on how good it sounds

I've only done 2 builds. Back when I was an early teen. I bought 2 of those light kits that made lights flash in time with the music. The instructions were a little fuzzy concerning the orientation of the rectifier. I put it in the way it looked good to me, but when I first went to turn it on, it blew up in a pile of smoke. The second one, I turned it around and it worked just fine.

One of the pluses the lured me to this system was that you really do not need to solder anything for the initial quick and dirty hookup. All of the connections between the boards are done with screw terminals. Soldering is an option of couse down the road for external run and trip leds, power switches, and binding posts.

The other thing that lured me was all of the positive comments, and the quality of the parts involved. The Heavy Duty Power Supply uses Nichicon 100V, 105C, 4700uF capacitors (very good quality Japanese capacitors). I priced them out online and the best price I could find was about $14 a pop when buying less than 50 of them at a time... The power supply board has 6 of them, and he sells the whole board for $65 before an additional discount if you buy a kit.

CDA-254. The 4 suffix designates 4 ohm stable. Although he only publishes it as 500W 8 ohm bridged, he does confirm it will also drive 4 ohm when bridged. Power will be slightly more, but not double. It will start clipping (>1% distotion) long before 1000W.

I think I might love this company. I was looking at the user manual, and noticed a VERY interesting rendition of the flag printed on the amp board...

So, Steve, a couple questions, if I may.

1. What's the functional difference between buying two of the CDA-245S kits and one of the CDA-2000 kits? They seem to be the same amp boards. Do you expect more power by using two (smaller?) power supplies and two (smaller?) toroids?

2. If you're using two of the CDA-245 in bridged mode, you're basically building two monobocks, right? I know it's a minor detail, but I don't see how you wire the external LED's in bridged mode.

1. What's the functional difference between buying two of the CDA-245S kits and one of the CDA-2000 kits? They seem to be the same amp boards. Do you expect more power by using two (smaller?) power supplies and two (smaller?) toroids?

2. If you're using two of the CDA-245 in bridged mode, you're basically building two monobocks, right? I know it's a minor detail, but I don't see how you wire the external LED's in bridged mode.

1) The 254S kit has a low profile power supply (smaller caps). I went with the heavy duty power supply. The power supply board will power both amps, and each amp will be bridged. The CDA-254 amp board actually has 2 amps on it, and I'm ordering 2 CDA-254 amps, and will bridge each one.

2) Yes. 2 monoblocks in 1 case with a shared 1000VA toroid. As far as the led's go, I think you just wire the left channel since that is the channel you will use when bridged. Not sure though.

The SDS was about $100 an amp more for things I did not need (balanced inputs, input level adjustment, etc.) The TI amps have greater distortion (their full power rating is actually at 10% distortion, vs. <1%), and were not as well received by the group. In reality, a lot of people preferred the sound of the SDS amp compared to the CDA amp, but most said it was not a difference that was worth the prices. Some people said it had "a deeper soundstage" and "presence". I tend to ignore comments by people who make those statements about amps.

The other thing that's kind of cool about the amp modules is the ease in switching form bridged to stereo mode. If it turns out that the M80 impedance is too low (it does seem to dip to 3 ohm) and the amp starts to overheat or cut out, I can always unbridge the amps by just changing a jumper and wiring the output from +V/+V on each amp, to +V/-V on each channel of the amp. I'd still have tons of power at 250W per channel, and now have 4 channels so I can also power the VP180 with it (and have 1 channel left over). It's a fallback position just in case.

Since this amp seems very simple to put together, if you really wanted to go DIY you could do component upgrades. Most of the time they are transformer or capacitor upgrades. Some believe that component upgrades can push "cheap" equipment with good circuitry designs into something that's great. Tried looking up mods for this amp, couldn't find much.

Class D amps don't take to tinkering with their designs too well. You really need to know what you're doing before you substitute any component. Else you end up building yourself a 1000 Watt AM radio station.

Sorry guys, I was out of town on business... Just got back and the box from ClassD was waiting for me! Quick shipping indeed! The toroidal transformer is coming directly from the manufacturer, so I hope it comes soon. I'll start mounting and wiring what I have so far tonight. Here's a couple of pix:

Since this amp seems very simple to put together, if you really wanted to go DIY you could do component upgrades. Most of the time they are transformer or capacitor upgrades. Some believe that component upgrades can push "cheap" equipment with good circuitry designs into something that's great. Tried looking up mods for this amp, couldn't find much.

Chris is right, you have to be careful with Class D type amps. Tom will upgrade the boards to whatever caps you want. You can either have him buy them, or mail the caps, etc. to him. He'll do the soldering for you. I asked Tom about an upgrade of the power supply caps from 4700uF caps to 10000uF caps. He said each one would cost about $15 more because he does not buy them in bulk. He said he would not recommend spending money on that though because it was just not worth it (I would not really hear any difference). I trusted his opinion and went with the stock caps. He did say that the toroid upgrade was a wise choice for multiple amps.

I can tell you from looking at what is on the board, these are high quality components.

Took about 2 hours, and it isn't the prettiest thing now, but I have it all wired now except for the toroid. Hoping it will come tomorrow of Saturday. I used 12 gauge wire to connect the power supply to the amps, and it was a tight fit (it's where I spent most of the time). I'll probably go with 14 gauge in the permanant installation.

Yes, the caps are my main worry Randy. I'll probably have to let it sit for a long while unplugged to let the caps discharge before I'm ready to take it apart for the final build.

The sockets are all screw down. Real easy.

Once the toroid arrives, my plan is to test it out first using my iPhone as the input, and my old VP150 as the sacrifical lamb before I even think about hooking it into my system. I'll test one channel at a time with the 6 ohm load of the VP150 and make sure everything looks good. If it all checks out, I'll hook it into my main system and have it drive both M80s using the AVR-3806 pre-outs.

Also, for the people who are interested, I noticed that the amp boards that I received did not have the Maron 560uF caps as shown on the picture on the ClassD site. A lot of people on the audiocircle board had commented on the lower quality of these caps in respect to the rest of the amp. Tom must have listened because they are now Panasonic 680uF caps. So again, I see a lot of high quality parts on these boards.

I just read through the manually and see how they are setup if you want to build external off/on switch as well as extending the leds. A little soldering possibly, but nothing to crazy. Man if this works out Steve and your happy with the performance and sound of D technology, I may have to consider this some day. Thanks for bringing this to our attention. Sure beats the heck out of the cost of other mfg'd amps with the same power. Are you going to build a mono version for the VP180 if all works out?

I'm hoping it sounds at least as good (but with more power) as the amp stage on the AVR-3806. I know, high hopes... But, if it works out that way I was considering a mono version for the VP180 in the short term, and in the long term buying exaclty what I bought again but wiring it unbridged to power the four surrond/rear channels. At that point, I would sell my AVR-3806 and buy a preamp/processor instead (something similar to the Emotiva UMC-1).

Looking very good. As I mentioned if this works out, there will be a number of sales from this build. Now just to decide on a chassis to put this into. Anyone found anything online. I could build a wood enclosure like others have done but I would like the manufactured look(steel/plastic/aluminum) to match the rest of the system

A guy named Jason (jtwrace) on the audiocircle board makes a case for this with everything pre-drilled and labeled. His gallery is here:

http://www.audiocircle.com/index.php?action=gallery;sa=album;id=4288

I have not contacted him yet, so I don't know the cost or if they are still available. I'm not sure if I'm going to build a case myself or go with something like that. You can however find some places online that have plain old aluminum or steel cases if you choose to drill yourself:

I'm hoping that the amp sounds great and he does get a lot of business becuase he seems like a nice guy who makes a nice product (I always like to see good quality parts being used). I know on the audiocircle site he gave that group a 5% discount. So, if after I put it together and it sounds good, I'll let him know about this board and see if he wants to offer a board discount to us.

Looking very good. As I mentioned if this works out, there will be a number of sales from this build. Now just to decide on a chassis to put this into. Anyone found anything online. I could build a wood enclosure like others have done but I would like the manufactured look(steel/plastic/aluminum) to match the rest of the system

This site looks interesting. You can fully design your own case and they can build it for you. I have no idea of the cost, but it looks pretty neat for those that don't have the means/knowledge for making his or her own.

Steve, that kit looks very cool. I'm eagerly awaiting your impressions. I like the fact that all the dirty work is kinda done already. I am certainly a novice when it comes to soldering and this seems like a good first project.

Steve which model did you get the 2000 kit?, man they have lots of kits and different model numbers, kinda confusing. I thought when bridged you could only drive 1 channel, or is that for each board you have?

Got a little antsy, so I dragged out my variable AC power supply and dialed it into about 50V AC to test the amps. I will say this... IT GETS LOUD! The sound seems about the same as the AVR-3806, but its hard to say because I'm just running one VP150 at a time. I hit 104db (@ 1m) constant output with the iPhone turned all the way up, and was pulling about 50W. Amp IC temp hovered around 56C (that's the actual chip, not the heatsink which was only warm to the touch). But just as I was typing this mail, the toroid arrived! Will be away for a bit doing some rewiring, but looking real good so far. Pix attached:

The M80s acutally got the amp heatsinks hot in bridged mode! I could sustain 102 db, both speakers, from 12 feet away no problem. The amp started going into protect mode (high heatsink temp over 100C) at about 105db sustained (my ears are ringing right now). What the amp does is turn off the affected channel until it cools and turns it back on again. I'm going to do a quick rewire to unbridge the amps to see how far I can push them. Some people had this problem and added to the heatsink and put a fan on it.

The sound is INCREDIBLE! It really does sound punchier than the AVR-3806. Very clear and tight. The wife said it was not even close (she liked it better than the AVR-3806), but it was a bit more close for me. Definitely punchier and tighter sound. If it sounds just as good unbridged with a higher output headroom before overtemp, I may leave it that way and hook the VP180 up now.

Okay, I've tested the system out and listened for several hours. I also hooked up the VP180 once I unbridged the amps. Here are my opinions.

Sound Quality - At least as good as the AVR-3806, and I think a good bit better. My wife thinks it's much, much better. Sound seems tighter and less muffled. I don't know if it's a characteristic of the Class D type amplification, having separate amplification, or a little of both. We switched back and forth between the AVR-3806 and the ClassD amp several times, and every time it felt like cotton came out of our ears.

Power - Here's the rub. I cannot test the unit to full power, even in unbridged mode, because the amps will cut due to high temperature. The best I was able to sustain without any cutouts was a constant 102db in my listening position. When I looked at the wattmeter, I was pulling about 90W. That's with 3 channels going too. Interestingly, the VP180 always cuts before the M80s. Maybe something changed with the new crossovers and drivers. The website (and the people on the board) have said that higher power demands require an active cooling system. When I shot the heatsink, it was at 73C constant. So, I think adding fins on the heatsink and the addition of a fan would allow me to bump the power up.

Fun Factor and Ease of Build - It's REALLY easy to build and a lot of fun. I'm really proud of it even in it's unfinished state. Knowing I can go in and tweak things (like thinking of a way to provide a more robust cooling solution) is a lot of fun for me.

Recommendation - I would recommend these kits for people who normally listen to music below 100db. If you listen in the 85-90db range, there is no problem whatsoever, and you can go with a much smaller toroid and amp size (driving the cost down even more). The sound quality, at least to our ears, easily rivals or beats that of high end professional equipment. I would also recommend this kit for someone looking to amplify surround speakers on the cheap, or someone who likes to tinker around (especially coming up with a nice cooling solution).

I'm going to keep the amp hooked into my system. I like the change in sound that much. Plus, I usually listen in the 90-95db range, so I'm good with the volume. I just want to be able to figure out a good way to get the most I can out of the amp modules... But hey, that's part of the fun right?

Keep us posted Steve. Curious, if you plan to call the seller and discuss the shutting down issue, if they claim 4ohm compatible, and shutting down when it is not within a case, plenty of ventilation?

My Odyssey mono's I had got fairly hot to the touch and were a A A/B design, which is not as efficient as Class D. I'm just trying grasp the concept of having all that power if you can only listen to levels the Denon will easily put out. I know the sound appears to be better/tighter overall, but as John always says, why have all that extra umph if you don't use it.

I have fabulous resistance to buying toys, mainly because I can never decide which toy to buy, and oh, it might go on sale, but now it's on sale, maybe I should, maybe I shouldn't, oh look, it's not on sale again...

But he said above even in unbridged mode it would still cut out because of overheating. I guess I'm just confused on if Class D is supposed to be 85-90+ efficient over A or A/B designs which are in the 50% or less range, no case for trapping the heat, and 4 ohm compatible, why the issues?

If there is a good sound improvement, for the price it still is a great dealeo.

But he said above even in unbridged mode it would still cut out because of overheating. I guess I'm just confused on if Class D is supposed to be 85-90+ efficient over A or A/B designs which are in the 50% or less range, no case for trapping the heat, and 4 ohm compatible, why the issues?

Are the heatsinks those little strips of silver metal in the pictures, or were the real heatsinks removed for the pics ?

A class AB (typical amp) with that power rating would have heatsinks the size of your head (ie a lot more than 10x the size of the heatsinks in the pics) wouldn't it ?

Yeah, I was kind of going back and forth on that--like Steve said, don't really need the balanced inputs or the gain knobs, but the heatsink sure would be nice. Not sure if it's $100 premium nice, though.

The heatsinks on all 3 amp boards (CDA, SDS, TI) are all extremely tiny, so I don't think even the SDS amp would have enough heatsink to drive them constantly at these volume levels without forced cooling. The CDA heatsinks measure 1/2" x 1" x 4.25" (a little over 2 cubic inches, the size of two kit-kat bars on top of each other). Looking at the heatsink in my AVR-3806, I'd say it has at least 50x the mass of the heatsink on these boards. The 4-channel amp I built totally assemlbed weighs about 25 lbs, 18 lbs of which is the toroid and 2 lbs for the mounting board. Most of the weight in my AVR-3806 appears to be heatsink (the tranformer is non-toroidal and much smaller).

I have absolutely no regrets on this purchase even with the reduced power output. 100db per channel of quality amplification with no external cooling is nothing to sneeze at, especially at this price and considering how small they are. It will be interesting to see what happens with the addition of more heatink and the addition of a fan or two.

Looks like the design's been changed a bit on the shipping amps--I see in his pictures that it has RCA jacks (maybe?) on the boards, but yours has screw terminals in those locations.

Yes, these came with screw terminals. He can build them with onboard RCA jacks instead, but most people do not want this since they will be putting the amps in an enclosure.

Originally Posted By: kcarlile

How'd you wire up the plug to the outlet? That would probably be the thing that would make me the most nervous.

I paralleled the primary of the toroid just as Tom said in the instructions. I used an old power cord I had lying around and cut off the female end. I wired the hot AC line through a 10A slo-blow fuse, to the line side of the primnary, and wired the neutral line to the neutral side of the transformer. Ground cord unused for now, but I would tie that to the chassis. (Warning - BIG pictures below)

On the secondary side, I had no directions for a 4-secondary transformer. So I wired secondaries 1 and 2 like his directions, and secondaries 3 and 4 like his directions. Since I wanted the voltage to remain constant, but with double the current, I connected these two discrete secondaries in parallel to the heavy duty power supply board. Worked great! (I put the electrical tape on the secondaries by the toroid for me to easily identify the wire pairs of the 4 secondaries, they are not really covering anything):

As a test, I directed my HEPA filter fan at the stock heatsinks. I was able to turn the receiver up to +7db with no cut outs and the amps stayed at about 78F. I was only able to hit about -3db on the receiver before. This volume was painfully loud, so I had to take pictures quickly and get out of the room. So, it's definitely something that can be fixed with better cooling.

Yep. The two halves of the speaker present their 4 ohm load at different frequency ranges, and have a higher impedence outside of their active ranges.

The problem is that without an electronic crossover you're sending all of the frequencies to both amps anyways, so you wouldn't get the benefits of a "real" bi-amp system that sends different frequency ranges to each amplifier.

But you do get the advantage of full voltage power to each side, rather than having that voltage split between the upper and lower sections, not sure if that makes alot of difference to SQ, might make it even a little tighter in the bass region.

True, (and I know this was discussed many times on this board years back), but since each "half" of the speaker is only really reproducing it's frequency range and not reproducing the frequencies outside of it's range, the speaker is actually drawing less power from each amp stage at any given setting on the receiver when I bi-amp right?

What I mean is, lets say I have the receiver at -12db. The high part of the speaker is dissipating, let's say 10W, and the low part of the speaker is dissipating, let's say 10W also. That means the single amp is "delivering" 20W.

If I leave the receiver setting at -12b, and change to bi-amp, both low and high still dissipate 10W, but now each amp is only "delivering" 10W.

In the end, if I had my sound meter measuring before and after, the sound level should be the same, right? And, I gained headroom on each amp.

I just thought of something. To bi-amp I would need to split the input signal, so the pr-amped signal voltage would be cut in half as well. I would then need to raise the receiver volume to get the same db output. The only was I guess this really works is to have a pre-amp voltage doubler as well.

Steve, I haven't been following this closely because I'm not very interested in DIY in general or class D amplifiers in particular, but I've now looked at the last couple pages. First point, as we've discussed at some length in the past, is that although two 8ohm loads driven in parallel result in a 4ohm net load, that isn't what's happening in a "4ohm" speaker. Say, at 100Hz if the impedance of a bass driver is actually 4ohms, because of the effect of the crossover circuitry the impedance of a "4ohm" tweeter section at that frequency might be more like 100ohms. The resulting impedance at 100Hz would then be 1/4+1/100=1/x; 25/100+1/100=1/x; 26/100=1/x; 26x=100; x=3.85ohms. So no, a "4ohm" speaker(which the M80s aren't at most frequencies, of course)isn't the result of two 8ohm sections being driven in parallel.

You ask "Am I missing something?" on the bi-amp question. Yes; although you refer to "each amp", there's only one in a two channel amplifier with one power supply section. The output transistors in each channel have no power of their own, and can't supply added "headroom".

Also, note on the voltage splitting question that two voltages in parallel don't form a voltage divider(series connection does that), and the output voltage to each load hasn't been cut in half.

If I leave the receiver setting at -12b, and change to bi-amp, both low and high still dissipate 10W, but now each amp is only "delivering" 10W.

Yes-ish, with the caveat that the split would probably be more like 4/16 than 10/10. Systems designed for bi- or tri-amplification generally have much larger amps for the woofers.

Originally Posted By: SRoode

In the end, if I had my sound meter measuring before and after, the sound level should be the same, right? And, I gained headroom on each amp.

Yes to the sound level, probably no to the headroom. There are a bunch of different ways an amplifier can "reach its limits" - output voltage, output current, temperature are the main ones. Most clipping happens when the amp reaches its voltage limit**, although shutdowns tend to happen as a result of current or temperature limits.

Since you don't have an electronic crossover before the amplifiers you're sending the same signal into both amps, and so the voltages will be the same and voltage limits will be hit at the same point as before.

If, however, the amp is "shutting down with 4 ohm load" as a result of current or overtemp limits, then the splitting of *current* could help a bit although this is where the 4/16 split bites you and you don't gain that much.

** it's actually not quite that simple because higher output currents tend to drag down the power supply voltage so you hit voltage clipping a bit sooner, but you get the idea...

Thanks for all of the great information guys, I'm really learning a lot. One thing I have not done is put my meter on the power supply to see if the voltage is drooping at high output. I would bet the toroid is just fine, but the DC power supply may be reaching it's limit. I'll try measuring on both sides of the dc power supply to see if the ac or dc (or both) dips on high output. I'm kind of hoping the dc output is drooping because that may be able to be fixed with the addition of another dc power supply (use one for each amp board).

I have affixed the additional heatsinks that I provided a link for several posts back on one of the amp boards. With no forced air cooling, the channel with the additional heatsinks is about 5 degrees C cooler than the one without. So, it's some progress.

I just ran a test with the left speaker "bi-amped", and the right speaker single amped. The "biamped" speaker can play with the receiver set 1.5 db higher before cutout than the single amped speaker. As bridgman predicted, when I raised the "bi-amped" speaker volume higher, it was the woofer amp that cut, while the mids and tweeters kept playing.

Neat. Sorry, I hadn't realized you were able to drive the amps hard enough for them to shut down, or I would have been a bit more enthusiastic about your bi-amping experiment

I guess someone not fighting a flu bug could probably use that 1.5 dB number and work out the actual power split between woofers and mid/tweeters, but that isn't going to be me, at least not for a few more days.

EDIT - I assume we're getting into REALLY FREAKIN' LOUD territory here. You might want to build a small insulated structure on the outside of your listening room similar to what Axiom uses for high volume testing.

We are in VERY loud territory here, but I wanted to see if I was getting what I "paid for". In reality, I do not think these amp modules can deliver 250W per channel @ 4 ohm, no matter what. I'd say they comfortably can deliver 60W per channel constant. The sound is definitely better than the AVR-3806 though. During normal listening conditions, I am keeping the receiver at -12db, which is about 87-90 db in the room. So, there is plenty of headroom. It has been a fun experiment though!

I'm using the amp in the bar area now. I did buy a switched mode power supply that seems to keep the amp "happier". I'm going to build an enclosure for the amp when I get some free time and keep it in the bar area permanently. I have my bluetooth receiver hooked into it, so I stream my iPhone music to it. It works pretty nicely.

I'm using the amp in the bar area now. I did buy a switched mode power supply that seems to keep the amp "happier". I'm going to build an enclosure for the amp when I get some free time and keep it in the bar area permanently. I have my bluetooth receiver hooked into it, so I stream my iPhone music to it. It works pretty nicely.

Well, I can't say I "love" the amp (I like it a lot), but it is a very nice amp for the price. I'm proud I was able to build it myself. In that regard, I think it will serve it's purpose entertaining guests in the bar area. It has not clipped with the new power supply.

Mr. Roode, congratulations on building an amp which did not burn your house down. You are a braver man than I am.

However, I am curious in that I have been informed by those who know that all well designed solid state amps perform identically within their specified performance paramters. Do you have any amps which have superior sound quality to your DIY effort?

The sound is INCREDIBLE! It really does sound punchier than the AVR-3806. Very clear and tight. The wife said it was not even close (she liked it better than the AVR-3806), but it was a bit more close for me. Definitely punchier and tighter sound. If it sounds just as good unbridged with a higher output headroom before overtemp, I may leave it that way and hook the VP180 up now.

So it is pretty close to his receiver's built in amp, just the performance increase you'd expect from more power.

The problem is, it gets outside of its specified performance parameters a little too easily with the power supply he was originally using.

I finally did finish off the amplifier! I bought an unfinished maple box on E-Bay for about$15, and drilled it out, then stained it. It took a good weekend to put everything together, but I'm really happy with it. I decided to use only one of the amp modules, so it's rated at 125W a channel 8 ohm, 250W a channel 4 ohm. The switched mode power supply is rated 500W continuous. I've been able to crank it all the way up and it does not trip out and sounds great. I keep it propped open slightly when I'm usingit so the air has a place to escape. It's a very low speed fan, almost silent, and the amp stays nice and cool (the heatsinks are barely warm to the touch). It's a nice little converation piece for the bar area.

Thanks guys! I hooked up the M80s as a final test. I ran the amp at full blast (I-phone was the pre-amp and source)for 2 hours. No tripping, 100db peak output at 1m (both speakers were running), and when I shot the heatsink with the infrared gun, it measured 94F. Not a bad little amp!

One thing I have noticed over the last week or so of listening is that the I-Phone just does not have enough "umph" to serve as an adeqaute pre-amp. When I hooked my Onkyo receiver up to the amp and used the pre-outs, I was really able to push the amp and the sound was great. So, I decided to hunt around for a little pre-amp (or headphone amp) for the amp I built. I finally decided on this one:

One thing I have noticed over the last week or so of listening is that the I-Phone just does not have enough "umph" to serve as an adeqaute pre-amp. When I hooked my Onkyo receiver up to the amp and used the pre-outs, I was really able to push the amp and the sound was great. So, I decided to hunt around for a little pre-amp (or headphone amp) for the amp I built. I finally decided on this one:

I actually saw that one and several others when I was looking around. The problem (for me) with the TC754 is that it is a 0 gain preamp, the volume control only attenuates. I needed something that would give me a pre-amp boost to help with the really low input signal of the I-phone. The pre-amp I ordered has a 20 db gain.

The Pre-amp arrived in the mail yesterday, on 12 days from Hong Kong, not too bad! The difference having a pre-amp in line with the amp is really night and day. I'm really able to drive the speakers now, and I have not even attempted to turn the volume all the way up (I have had it as high as about 60% and that was more than enough). I've also tried using it as a headphone amplifier and it sounds great that way as well. There are only 2 issues I have with it, and I knew about them before I bought it. First, the black heatsinks get INCREDIBLY hot. I shot them with my infrared thermometer, and they were about 75C. Since this is a class A amp, it seems to always be this temperature when on, regardless of the listening volume. Supposedly this temperature is okay. The next issue is interference. Since the amp is not in a shielded enclosure, you do not want to bring yor iPhone within about 8 feet of this amp. One of the guys on another board fixed this by plating the top and bottom acrylics with aluminun foil and tying it all to a common ground. I may enclose it in the future, but for now it's okay since I play music from my iPhone to a Bluetooth receiver... No issues with that.